The increased health risks associated with smoking during pregnancy for mothers and babies are well-documented. Now a new study published in the journal Human Reproduction suggests that mothers who continue to smoke while pregnant could damage the future fertility of their sons.
Previous studies have linked smoking during pregnancy to an increased risk of nicotine dependence among the daughters of female smokers. The present study investigates sex differences associated with fertility among male and female offspring.
To study the effects of smoking during pregnancy on fertility, researchers led by Professor Eileen McLaughlin of the University of Newcastle in Australia used a comprehensive mouse model with carefully controlled environments and exposure to toxic chemicals. The team used an animal model because similar studies on human participants are unethical.
Explains Professor McLaughlin:
“It would be unethical to deliberately expose pregnant mothers and their offspring to the toxins in cigarettes – we already know that smoking in pregnancy harms the baby in the womb – as babies are often born small and vulnerable to disease. So, in this study we used a mouse animal model, which directly mimics human smoking, to look at what effects the mothers smoking during pregnancy and breast feeding has on the fertility of their male pups.”
The researchers developed a machine that draws smoke into a nose piece and then placed 27 female mice into the machine to inhale the smoke into their lungs. The machine mimicked the way in which humans inhale smoke while smoking a cigarette. The mice inhaled the equivalent of a pack of 24 cigarettes a day in humans.
The researchers also exposed another 27 female mice to normal air.
After six weeks of using the smoke machine on half the mice, the researchers placed the females with males to produce litters. The female mice produced a total of 108 male offspring.
For the exposed mice, smoking continued throughout pregnancy and lactation until weaning.
To determine the effects, if any, of smoking during pregnancy on the fertility of the 108 male offspring, the researchers looked at damage to the DNA of cells involved in the process of producing sperm, sperm counts, and the shape and motility of the sperm as well as the ability of the male offspring to produce additional offspring.
The researchers found that the male offspring of mothers who smoked while pregnant exhibited increased rates of subfertility (lowered fertility) and infertility (lack of fertility). In other words, smoking during pregnancy can harm the fertility of male offspring.
States Professor McLaughlin:
“Our results show that male pups of ‘smoking’ mothers have fewer sperm, which swim poorly, are abnormally shaped and fail to bind to eggs during in vitro fertilisation studies. Consequently, when these pups reach adulthood they are sub fertile or infertile. This is the first time we have been able to prove conclusively that male baby exposure to cigarette toxins in pregnancy and early life will damage later life fertility.”
One reason for the decreased fertility among the male offspring of smoking mothers is that cigarette toxin exposure affects the stem cell population in the testes:
“We now know that exposure to cigarette toxins directly affects the stem cell population in the testes, causing a permanent reduction in the population of sperm produced. We also know that oxidative stress induced by these toxins causes damage to the nuclei and mitochondria (the cell’s ‘power’ supply) of cells in the testes and this results in sperm with abnormal heads and tails, that are unable to swim properly or successfully bind and fuse with eggs.”
Although the mouse model used in the present study has limitations, the results may likely have wider implications for human health:
“Although this is a study in mice, the findings are relevant to human health as many men, now in their 30s and 40s, were exposed to cigarette toxins in the womb when it was less well known that smoking affected babies’ health. These men have difficulty conceiving and this is associated with production of low numbers of poor quality sperm in their semen. Unfortunately about 25% of young women today continue to smoke when they are pregnant and/or breast feeding – thereby potentially damaging their sons fertility.”
Women are advised to quit smoking prior to conception to reduce the risk of health problems associated with smoking during pregnancy.
Damaging legacy: maternal cigarette smoking has long-term consequences for male offspring fertility: http://humrep.oxfordjournals.org/content/early/2014/09/24/humrep.deu235.abstract
Damaging legacy: mothers who smoke affect the fertility of their sons: http://www.alphagalileo.org/ViewItem.aspx?ItemId=145732&CultureCode=en
Smoking during pregnancy could damage sons’ fertility: http://www.medicalnewstoday.com/articles/283217.php
Smoking During Pregnancy and Male Fertility: http://www.freeimages.com/photo/30214